The program objective is to facilitate the management of the NIH Animal Genetic Resource (NIHAGR) through development and utilizaton of embryo collection, culture, freezing and transplantation as techniques for cryobanking genetic material and improving reproductive potential. The NIHAGR consists of several laboratory species for which cryobanking is ongoing in mice and being developed in rabbits. Cryobanking is confounded by unique genotypic responses to cryopreservation found in over 30 mouse genotypes investigated to date. Embryos are frozen in a programable unit at species specific rates to ensure embryo survival. A cryoprotectant in the freezing medium allows sufficient dehydration to protect the blastomeres during freezing. Following thawing and dilution of the cryoprotectant, embryos are cultured to assess in vitro development. Transplantation of embryos into recipient females monitors in vivo development. In vitro fertilization and ova freezing are being examined as tehcniques to salvage limited genetic material from single females or strains with poor in vivo fertilizatiaon rates. Banked embryos are maintained in a frozen state until needed for rederivation. Concurrent comparative research studies are designed to identify modifications in methodology which will enhance female response to ovulation induction regimens, improve post-thaw embryo survival and examine the influence of genotype on embryo cryopreservation.